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Why is oceanic crust younger than about 200 million years?

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Watch Earth's Continents Move — paleogeography Watch a time-lapse of Earth changing through geologic time, from the Cambrian Era to the projected period of Pangea Proxima.

In the context of paleogeography, oceanic crust is younger than approximately 200 million years because it is continuously recycled through the process of plate tectonics.12

New oceanic crust is constantly generated at oceanic ridges through seafloor spreading, where magma rises from the mantle to form new seafloor. As this crust moves away from the spreading centers, it cools, becomes denser, and is eventually consumed or "recycled" back into the Earth's interior at subduction zones.3452

Because this cycle of creation and destruction is ongoing, the oceanic lithosphere is relatively transient compared to continental lithosphere, which is less dense and not easily subducted, allowing it to preserve rocks dating back billions of years. While older fragments of oceanic crust, known as ophiolites, can be found thrust above sea level, the active oceanic crust currently forming the ocean basins is geologically young.21